Association of Second and Early Third Trimester Cervical Length With Prolonged Pregnancy in Asymptomatic Women at Risk of Preterm Birth

Objectives

To determine if transvaginal ultrasound cervical length (CL) in the second (T2) (16⁰–23⁶ weeks) or early third trimester (T3) (24⁰–29⁶ weeks) in individuals at increased risk of preterm birth (PTB) is associated with prolonged pregnancy (≥41⁰ weeks), and if there is a specific CL cut-off that is predictive.

Methods

This retrospective cohort study included individuals with singleton gestations; and a history of spontaneous PTB, excisional treatment of the cervix or uterine anomaly, undergoing transvaginal ultrasound CL 16⁰–29⁶ weeks. Results were divided by CL quartile in T2 and T3 separately.

Results

Overall, 914 individuals were included, 514 having CL assessment in T2 and 857 in T3. In T2, those with CL in quartiles 2, 3, and 4 were more likely to have a prolonged pregnancy compared with quartile 1 (adjusted OR [aOR] 2.47, P = 0.049; aOR 3.15, P = 0.009; aOR 2.73, P = 0.028, respectively). However, the T2 receiver operator characteristic (ROC) area under the curve (AUC) (0.572) did not reach statistical significance (P = 0.057). In T3, those with CL in quartiles 3 and 4 were more likely to have a prolonged pregnancy compared with quartile 1 (aOR 2.42, P = 0.021; and aOR 3.10, P = 0.002, respectively). The T3 ROC curve reached statistical significance (P = 0.002, AUC = 0.622) but did not meet the criteria for a good screening test based on the AUC value. Subgroup analysis of those with a previous spontaneous PTB found the T2 ROC curve to be promising (AUC = 0.700, P = 0.013).

Conclusions

In individuals at risk of PTB, longer CL in T3 may be a better predictor of prolonged pregnancy than T2 but does not appear to be a good screening test in either gestational period. Further research is suggested in those with a history of PTB.